As illustrated in FIG. 41, a steering apparatus for an automobile is constructed such that rotation of the steering wheel 1 is transmitted to an input shaft 3 of a steering gear unit 2, and as the input shaft 3 rotates, pushes or pulls a pair of left and right tie rods 4, which applies a steering angel to the front wheels. The steering wheel 1 is supported by and fastened to the rear end section of a steering shaft 5, and the steering shaft 5 is inserted in the axial direction through a cylindrical steering column 6 and is supported by the steering column 6 so as to be able to rotate freely. Moreover, the front end section of the steering shaft 5 is connected to the rear end section of an intermediate shaft 8 by way of a universal joint 7, and the front end section of the intermediate shaft 8 is connected to the input shaft 3 by way of another universal joint 9. In this specification, unless specially indicated, the forward-backward direction, left-right direction and up-down direction, are the forward-backward direction, the left-right direction and the up-down direction of the vehicle.
This steering apparatus is provided with a tilt mechanism for adjusting the up-down position (tilt position) and a telescoping mechanism for adjusting the forward-backward position (telescopic position) of the steering wheel 1 according to the size and driving posture of the driver, which has conventionally been performed. Of these, in order to construct this tilt mechanism, the steering column 6 is supported by the vehicle 10 so as to be able to pivotally displace around a pivot shaft 11 that is placed in the left-right direction. Moreover, a displacement bracket 18 that is fastened to a portion near the rear end of the steering column 6 is supported by a support bracket 12 that is supported by the vehicle 10 so as to be able to displace in the up-down direction and forward-backward direction. On the other hand, in order to construct the telescopic mechanism, the steering column 6 is constructed by combining an outer column 13 and an inner column 14 in a telescopic shape so as to be able to expand and contract freely, and the steering shaft 5 is constructed by combining an outer shaft 15 and an inner shaft 16 with a spline fit so as to be able to transmit torque and so as to be able to expand and contract freely. In the example in the figure, an electric power-steering apparatus is also assembled in which an electric motor 17 as an auxiliary power source is able to reduce the force necessary for operating the steering wheel 1.
In the case of construction of a manual tilt mechanism and telescopic mechanism which is not equipped with an electrically-operated apparatus, it is possible to adjust the position of the steering wheel and to secure the steering wheel 1 after adjustment based on operation of an adjustment handle. Various kinds of construction for this kind of manual tilt mechanism or telescoping mechanism are known. For example, in the case of the construction illustrated in FIG. 41, long holes 19 for telescopic mechanism that are long in the axial direction of the outer column 13 are formed in the displacement bracket 18 to which the outer column 13 is fastened. Moreover, the support bracket 12 comprises a pair of support plate sections 20 that hold the displacement bracket 18 on both the left and right sides, and long holes 21 for tilt mechanism that are long in the up-down direction are formed in portions of these support plate sections 20 that are aligned with each other. In general, the long holes 21 for tilt mechanism have a partial arc shape that is centered around a pivot shaft 11. An adjustment rod 22 is inserted through the long holes 19 for telescopic mechanism and the long holes 21 for tilt mechanism. A pair of pressing sections are provided on the adjustment rod 22 such that they are located on both the left and right sides of the pair of support plate sections 20, and an expansion and contraction mechanism that operates based on the operation of the adjustment handle 23 (see FIG. 1 to FIG. 3) makes it possible to expand or contract the space between these pressing sections.
When adjusting the up-down position or the forward-backward position of the steering wheel 1, by turning the adjustment handle 23 in a specified direction, the space between the pair of pressing sections is expanded. As a result, the friction force that acts between the inside surfaces of the pair of support plate sections 20 and the outside surfaces of both the left and right sides of the displacement bracket 18 is reduced. In this state, the tilt position and the telescopic position of the steering wheel 1 can be adjusted within the range that the adjustment rod 22 can displace within the long holes 19 for telescopic mechanism and the long holes 21 for tilt mechanism. After adjustment, by turning the adjustment handle 23 in the opposite direction from the specified direction, the space between the pair of pressing sections is contracted. As a result, the friction force is increased, and it becomes possible to maintain the steering wheel 1 in the adjusted position.
In this kind of steering apparatus, during a collision accident, when a secondary collision occurs where the body of the driver collides with the steering wheel 1, in order to lessen the impact load on the driver, a mechanism is provided that allows the steering wheel 1 to displace in the forward direction. More specifically, construction is employed wherein the support bracket 12 is supported by the vehicle 10 so that it can break away in the forward direction due to impact during a secondary collision. In the case of a steering apparatus with this kind of construction, when the force for maintaining the steering wheel 1 in the adjusted position, or in other words, the force for maintaining the outer column 13 in the support bracket 12 is weak, there is a possibility that the outer column 13 will move in the forward-backward direction (telescopic direction) or the up-down direction (tilt direction) with respect to the support bracket. When the outer column 13 moves with respect to the support bracket 12, how the impact from the outer column 13 is applied to the support bracket 12 changes, so there is a possibility that designing the impact absorbing mechanism in order that the support bracket 12 breaks away from the vehicle 10 will become difficult.
On the other hand, in order to increase the force by which the support bracket 12 holds the outer column 13 without increasing the operating amount or operating force of the adjustment handle, preferably the number of friction surfaces for maintaining the holding force is increased. JP 10-35511 (A) discloses construction where the number of friction plates is increased by combining in a friction plate that is supported by the steering column and a friction plate that is supported by the support bracket. However, in this kind of construction, the friction plates are supported by the steering column or support bracket such that only displacement in the left-right direction is allowed. Consequently, in order to increase the number of friction surfaces, a plurality of friction plates is necessary. Therefore, as the number of friction surfaces increases, the increase in the resulting dimension in the left-right direction, the number of parts and the weight becomes large.
JP 2010-52639 (A) discloses construction for preventing displacement of the steering column in the upward rear direction along the direction of inclination of the long holes for tilt mechanism during a secondary collision by increasing the inclination angle of the long holes for tilt mechanism with respect to an virtual plane that is orthogonal to the center axis of the steering column so that it is greater than the inclination angle of the long holes for tilt mechanism with respect to the forward-backward direction of the center axis of the steering column regardless of the up-down position of the steering wheel.